Wafer level package of MEMS sensor and method for manufacturing the same

ABSTRACT

A MEMS sensor and a manufacturing method thereof is provided: forming a lower electrode layer wherein a metal is deposited on a portion of a lower glass substrate; forming a structural layer by etching according to a pattern which is formed on an upper surface of a silicon wafer and then further etching to the same thickness as the metal which is formed on a portion of the lower electrode layer; anodic bonding the structural layer to an upper portion of the lower electrode layer formed; forming a sensing part in the structural layer by etching according to a pattern which is formed on an opposite surface of the structural layer which is not etched; and forming an upper electrode layer by depositing a metal on an upper wafer and eutectic bonding the upper electrode layer to the structural layer on which the sensing part is formed.

CROSS-REFERENCE(S) TO RELATED APPLICATION

The present claims priority of Korean Patent Application Number10-2013-0158742 filed on Dec. 18, 2013, the entire contents of which areincorporated herein for all purposes by this reference.

BACKGROUND Technical Field

The present disclosure relates to a wafer level package of aMicro-Electro Mechanical Systems (MEMS) sensor and a method formanufacturing the same, and more specifically, to a wafer level packageof a MEMS sensor and a method for manufacturing the same whereininterference can be removed when bonding a MEMS structural layer to alower and an upper electrode layers.

Background Art

MEMS (Micro Electro-Mechanical System) refers to a micro-miniatureelectronic mechanical element technology which ranges in size frommillimeters to micrometers based on a process technology ofsemiconductor. A MEMS element generally consists of a driving partincluding a mechanical structure and a control part including anelectric circuit. In particular, its performance stability is known todeteriorate due to an influence from external moisture and dust.Additionally, as in an angular velocity sensor, when high speedoperation of a driving part is required, the element performance maydeteriorate due to a damping effect by the resistance of the air insideof the element. Accordingly, a hermetic sealing thereof is essential inorder to minimize the influence of external factors.

Some known hermetic sealing technologies that are used at wafer levelinclude anodic bonding, eutectic bonding, etc. Anodic bonding is usedfor bonding a glass to silicon, in which temperature and voltage areapplied to an upper wafer and a lower wafer to bond the surface tightly.Products that are anodicly bonded have excellent sealing properties andhigh boding strength. Eutectic bonding is used for bonding wafers to aneutectic alloy, such as an interlayer. In eutectic bonding, the bondingtemperature is low and a stress from thermal expansion is lowrelatively.

Recently, with a trend of downsizing of electronic device, MEMS elementshave been required to be packaged at a higher density. However,conventional technology of packaging a plurality of elements on asubstrate has limitations. Specifically, in case of elements where ahigh speed operation is performed like an angular sensor, when foreignmatters are attached to the element while dicing the wafer that has beenprocessed, its performance may deteriorate. In order to overcome thesedrawbacks, a stacked type packaging technology capable of stacking aplurality of wafers in a three dimensional way is required.

The description provided above as a related art of the present inventionis just for helping in understanding the background of the presentinvention and should not be construed as being included in the relatedart known by those skilled in the art.

SUMMARY OF THE DISCLOSURE

The present invention has been proposed to solve the above drawbacks andone object of the present invention is to provide a wafer level packageof a MEMS sensor and a method for manufacturing the same capable ofpackaging three story wafers using a double bonding technique wherein ananodic bonding and an eutectic bonding are combined.

In order to achieve the above object, a method of manufacturing a waferlevel package of a MEMS sensor according to the present invention isprovided. In particular, a lower electrode layer is formed wherein ametal is deposited on a part of a lower glass substrate and a structurallayer is formed by etching a silicon wafer according to a pattern whichis formed on an upper surface of the silicon wafer and then furtheretching the silicon wafer to a same thickness as the metal which isformed on a part of the lower electrode layer. Next, the g thestructural layer is anodic bonded to an upper part of the formed lowerelectrode layer and a sensing part is formed in the structural layer byetching according to a pattern which is formed on an opposite surface ofthe structural layer which is not etched. Subsequently, an upperelectrode layer is formed by depositing a metal on an upper wafer andthe upper electrode layer is eutectic bonded to the structural layer onwhich the sensing part is formed.

More specifically, the step of forming the structural layer may includeetching so that the height of a part of the structural layer, with whicha part of the lower electrode on which the metal is formed is incontact, is different from the height of another part of the structurallayer with which a part of the lower electrode on which the metal is notformed is in contact.

The step of forming the sensing part may further include a step ofetching by forming a pattern identical to a pattern formed on an uppersurface of the silicon wafer on a part which is not anodic bonded amongthe structural layer. Additionally, the step of forming the sensing partmay be performed by forming a pattern of the sensing part on the partthat is etched and etching according to the pattern formed.

In some exemplary embodiments, the upper electrode layer formed bydepositing a metal on the wafer may be formed by etching along a patternwhich is formed on the upper wafer and depositing a metal on the upperpart of the plating layer for plating the upper wafer etched. Inaddition, the step of eutectic bonding with the structural layer may beperformed by eutectic bonding the upper electrode layer to one surfaceof the structural layer on which the sensing part is formed.

As such, the above wafer level package of a MEMS sensor may include: alower electrode layer wherein a metal is formed on a part of a glasssubstrate; a structural layer which is formed by etching according to apattern formed on an upper surface of a silicon wafer and thenadditionally etching to the same thickness as a metal formed on thelower electrode layer, and is anodic bonded to the lower electrodelayer; a sensing part formed in the structural layer by etchingaccording to a pattern which is formed on an opposite surface of a partthat is not etched among the structural layer; and an upper electrodelayer which a metal is formed on the silicon wafer and is eutecticbonded to the structural layer on which the sensing part is formed.

The wafer level package of a MEMS sensor may further include a platinglayer which is formed between the silicon wafer and the metal formed onthe silicon wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 17 are views showing the method for manufacturing a waferlevel package of a MEMS (Micro Electro Mechanical Systems) sensor in atime series according to an embodiment of the present invention.

DETAILED DESCRIPTION

The special configurations and functional descriptions are merelyexemplary for describing the embodiments according to the presentinvention, and further the embodiments of the present invention may bereplaced by various modifications, and thus it should not be construedas limiting thereto.

The embodiments according to a concept of the present invention may bechanged variously and have various types and thus the specialembodiments will be illustrated in the drawings and described in thespecification. However, the embodiments according to a concept of thepresent invention are not limited to the specifically disclosed typesand thus it should be understood that it includes all modifications andequivalents or replacements included within a spirit and a scope of thepresent invention.

Although terms like a first and a second are used to describe variouscomponents, but the components are not limited to these terms. Theseterms are used only to differentiate one component from another one, forexample, the first component can be referred to as the second component,or the second component can be referred to as the first component,without departing from the scope of the present invention.

It also should be understood that when it is stated that one componentis “connected or “coupled to another component, even though the onecomponent may be directly connected or coupled to another component, butthere may be other components between them. However, it has to beunderstood that when it is stated that one component is “directlyconnected” or “directly coupled” to another component, there is nointermediate component between them. The terms used for describing arelation among other components, that is, “between”, “right between”,“adjacent to” or “directly adjacent to” should be construed similarly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting to the embodiments.As used herein, unless otherwise defined, the singular forms “a,” “an”and “the” are intended to include the plural forms as well. Unless thecontext indicates otherwise, it will be further understood that theterms “comprises” and/or “having” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, parts or combination thereof.

All terms including technical or scientific terminology used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which example embodiments belong. It will be further understoodthat terms, such as those defined in commonly used dictionaries, shouldbe interpreted as having a meaning that is consistent with their meaningin the context of the relevant art and will not be interpreted in anidealized or overly formal sense unless expressly so defined herein.

Hereinafter, reference numerals will now be made in detail to variousembodiments of the present invention, examples of which are illustratedin the accompanying drawings and described below. In the drawings, thesame reference numerals refer to the same components.

FIGS. 1 to 17 are views showing the method for manufacturing a waferlevel package of a MEMS (Micro Electro Mechanical Systems) sensoraccording to an exemplary embodiment of the present invention.

The method for manufacturing a wafer level package of a MEMS (MicroElectro Mechanical Systems) sensor according to an exemplary embodimentof the present invention may for example include: forming a lowerelectrode layer 100 on which a first metal 14 c is deposited on aportion of a lower glass substrate 10; forming a structural layer 200 byetching a silicon wafer 20 according to a pattern 22 a which is formedon an upper surface of the silicon wafer 20 and then further etching thesilicon wafer 20 to a same thickness as the metal 14 c which is formedon a portion of the lower electrode layer 100; anode-bonding thestructural layer 200 to an upper portion of the formed lower electrodelayer 100; forming a sensing part 50 in the structural layer 200 byetching according to a pattern 22 c which is formed on an oppositesurface of the structural layer 200 which is not etched; and forming anupper electrode layer 300 by depositing a metal 34 a on an upper wafer30 and eutectic-bonding the upper electrode layer 300 to the structurallayer 200 on which the sensing part 50 is formed.

In detail, referring to FIG. 5, when forming the structural layer 200, apattern 22 b may be applied again after the etching instead of thepattern 22 a that have been used for previous etching in order to etchadditionally to the same thickness as the metal which is formed on aportion of the lower electrode layer 100. As the pattern 22 b isapplied, the metal 14 c which is formed on a portion of the lowerelectrode layer 100 may be bonded to a portion which is etchedadditionally when the anodic bonding is performed. That is, the heightof a portion of the structural layer 200 with which a portion of thelower electrode layer 100 on which the metal 14 c is formed is incontact may be different from the height of another portion of thestructural layer 200 with which a portion of the lower electrode onwhich the metal 14 c is not formed is in contact.

The etching of the lower electrode layer 100 shown in FIG. 1 and FIG. 2is performed by forming a photo sensitive film pattern 12 on a glasssubstrate 10 and etching a portion of the glass substrate 10 using thephoto sensitive film pattern 12 as a mask, and a trench is formedaccording to the etching. For the photo sensitive film pattern 12, anegative photo sensitive film of about 2 μm is used, and when formingthe photo sensitive film pattern 12, a hard baking process applied priorto being applied. Additionally, it is preferable to form the trench at adepth of about 200 nm by performing a wet etching process for about 5 to7 minutes using 6:1 BOE solution. Such an etching method may be appliedidentically during the etching processes shown in FIGS. 3 to 5.

Subsequently, the metal layers 14 a, 14 b, 14 c are formed on the trenchand the photo sensitive film pattern 12 and the photo sensitive filmpattern 12 is removed by wet etching, so that only the metal 14 c formedon only a portion of the lower electrode 100 remains, as shown in FIG.2. As the metal 14 c, Chrome (Cr) or Aurum (Au) may be used, and it ispreferable that the thickness be about 30˜60 nm and about 300˜400 nm,respectively.

Referring to FIG. 6, anodic bonding is performed by inversing thestructural layer 200 shown in FIG. 5 on the lower electrode layer 100 ona portion of which the metal 14 c is formed. Such an anodic bonding isperformed by applying voltage of about 700V to 900V to the lowerelectrode layer 100 and providing temperature of about 300 to 450° C. toa bonding portion wherein it may be useful to provide a sealed bondbetween a silicon wafer 20 of the structural layer 200 and the glasssubstrate 10. In detail, the anodic bonding may be performed for about40 minutes at temperature of about 300° C., pressure of about 600 mbar,and voltage of about 700V.

Thereafter, as shown in FIG. 7, the silicon wafer 20 may be etched byforming a pattern 22 c which is identical to the pattern formed on anupper side of the silicon wafer 20 on the other side of the structurallayer 200 on which the anodic bonding has not been applied. The etchingmethod is the same as described above. After that, as shown in FIG. 8, asensing part 50 shown in FIG. 9 is formed by forming a pattern 22 d ofthe sensing part 50 on an etched portion and etching according to thepattern formed.

Meanwhile, as shown in FIGS. 10 to 11, in the upper electrode layer 300a trench is formed by forming a pattern 22 e on the upper wafer 30 andetching, and a plating layer 32 is formed by removing the pattern 22 eand then plating copper on the upper wafer 30. After that, a metal 34 amay be formed on a portion of the plating layer 32 using the patternagain. Only a portion of the entire metal layer (34 a, 34 b) will afterthe pattern is used.

After that, as shown in FIG. 13, the upper electrode layer 300 may beeutectic bonded to the structural layer 200 on which the sensing part 50is formed. Specifically, the eutectic bonding may be performed for about15 minutes at temperature of about 400° C. and pressure of about 4000mbar. That is, the temperature, pressure and time period are differentbetween the anodic bonding and the eutectic bonding so these bondingshave no influence on each other. When the lower electrode layer 100 andthe structural layer 200 are eutectic bonded, and then the structurallayer 200 and the upper electrode layer 300 are eutectic bonded again,eutectic temperature are identical, therefore an eutectic bonding layerwhich has been formed between the lower electrode layer 100 and thestructural layer 200 may be melted again. Such problems may causeelectrical connection of melted bonding metals or failure of thealignment between the substrates when a pressure is applied.Accordingly, according to an embodiment of the present invention, theproblems described above may be resolved by bonding the lower electrodelayer 100, the structural layer 200 and the upper electrode layer 300using an anodic bonding and an eutectic bonding, respectively.

According to an additional structural layer shown in FIGS. 14 to 17, aportion to be connected to the plating layer 32 is etched using apattern 22 f. At this time, before etching, a new plating layer which isconnected to an existing plating layer 32 may be formed at the oppositesurface of the upper electrode layer 100 on which the plating layer 32is formed. Additionally, a metal 60 may be deposited on the upperelectrode again for an electrical wiring, and a wafer level package 400of MEMS sensor, all processes of which are completed as shown in FIG.17, may be obtained by forming a pattern 22 a again on an electricalwiring 60 and etching the pattern.

According to a wafer level package of MEMS sensor and a method formanufacturing the same of the present invention, the respective bondingconditions are different when the lower electrode layer is bonded to aMEMS structure and the upper electrode layer is bonded to the MEMSstructure, thereby not influencing to each other.

That is, when a bonding of the lower electrode layer with the MEMSstructure is defined as primary bonding and a bonding of the upperelectrode layer with a MEMS structure is defined as secondary bond,wafer alignment error during primary bonding which has been bondedalready can be prevented when the secondary bond is performed.Additionally, after the secondary bond is completed the step of theprimary bonding can be reduced or the connection of each metal can beprevented. Further, the number of metal layers to be deposited can bereduced in comparison to a conventional method in order to lower theunit price of the process.

Although the present invention was described with reference to specificembodiments shown in the drawings, it is apparent to those skilled inthe art that the present invention may be changed and modified invarious ways without departing from the scope of the present invention,which is described in the following claims.

What is claimed is:
 1. A method for manufacturing a wafer level packageof a MEMS sensor comprising: forming a lower electrode layer wherein afirst metal is deposited on a portion of a lower glass substrate;forming a structural layer by etching a silicon wafer on one sidesurface according to a first pattern which is formed on an upper surfaceof the silicon wafer and then further etching the silicon wafer to asame thickness as the first metal which is formed on the portion of thelower glass substrate of the lower electrode layer; anodic bonding thestructural layer to an upper portion of the formed lower electrodelayer; forming a sensing part in the structural layer by etchingaccording to a second pattern formed on a second side surface of thestructural layer opposite to a first side surface of the structurallayer bonded to the lower electrode layer; and forming an upperelectrode layer by depositing a second metal on an upper wafer andeutectic bonding the upper electrode layer to the structural layer inwhich the sensing part is formed.
 2. The method for manufacturing awafer level package of a MEMS sensor of claim 1, wherein the upperelectrode layer formed by depositing the second metal on the upper waferis formed by etching along a fourth pattern which is formed on the upperwafer and depositing a third metal on an upper portion of a platinglayer for plating the upper wafer etched.
 3. The method formanufacturing a wafer level package of a MEMS sensor of claim 2, whereineutectic bonding with the structural layer is performed by eutecticbonding the upper electrode layer to one surface of the structural layerin which the sensing part is formed.